We show that the Malčev Lie algebra of the fundamental group of a compact 2n+1-dimensional Sasakian manifold with n≥2 admits a quadratic presentation by using Morgan’s bigradings of minimal models of mixed-Hodge diagrams. By using bigradings of minimal models, we also simplify the proof of the result of Cappelletti–Montano, De Nicola, Marrero and Yudin on Sasakian nilmanifolds.